Prep the pan and oven. Heat oven to 325°F (165°C). Line the bottom of a 9-inch springform pan with parchment.
Lightly grease the sides. If using a water bath, wrap the outside of the pan with two layers of foil to prevent leaks.
Make the crust. In a bowl, combine finely crushed Oreos, melted butter, and a pinch of salt. Mix until the crumbs feel like wet sand.
Press and par-bake. Press the crumb mixture firmly into the bottom of the pan, pushing slightly up the sides.
Use a flat-bottomed glass for an even layer. Bake for 8–10 minutes, then set aside to cool slightly.
Blend the cream cheese base. In a large bowl, beat the cream cheese on low to medium speed until smooth and no lumps remain, about 1–2 minutes. Scrape down the bowl often to avoid clumps.
Add yogurt and sugar. Mix in the Greek yogurt and sugar (or substitute) until fully combined.
Keep the mixer speed low to limit air bubbles.
Incorporate protein and dry ingredients. Whisk protein powder, cornstarch, and salt together in a small bowl to break up clumps. Add to the batter and mix on low until just smooth. The cornstarch helps stability and a clean slice.
Add vanilla and eggs. Beat in vanilla, then add eggs one at a time, mixing on low just until combined after each.
Avoid overmixing; too much air leads to cracks.
Fold in Oreos. Gently fold in the chopped Oreos with a spatula. Don’t crush them too much—larger pieces give a nice cookies-and-cream texture.
Pour and settle. Pour batter over the crust. Tap the pan on the counter a few times to release any air bubbles.
Prepare the water bath (optional but helpful). Place the springform pan into a larger roasting pan.
Pour hot water into the roasting pan to come halfway up the sides of the springform. This promotes even baking and prevents cracks.
Bake low and slow. Bake at 325°F (165°C) for 45–55 minutes. The edges should be set, and the center should still have a slight jiggle, like Jell-O.
Avoid overbaking.
Cool gradually. Turn off the oven, crack the door, and let the cheesecake rest inside for 45 minutes. Then remove from the oven and water bath. Run a thin knife around the edge to loosen.
Cool to room temperature for 1 hour.
Chill to set. Cover and refrigerate for at least 6 hours, but preferably overnight. This step fully sets the proteins and improves flavor.
Add optional topping. Spread the sweetened Greek yogurt over the chilled cheesecake and finish with crushed Oreos. Slice with a hot, clean knife for neat cuts.